The 4 mammalian BMP-l-like proteases (BLPs) play central roles in forming the ECM through biosynthetic processing of precursors, and enhance BMP signaling by cleaving the extracellular antagonist Chordin. Here we show BLPs to cleave prodomain sequences of the TGF-b-like factor gdf-8 (myostatin). Secreted gdf-8 is normally noncovalently bound to its prodomain in a latent complex. Cleavage of prodomain sequences by BLPs is shown to activate gdf-8. Golf-8 inhibits muscle growth, and mutation of the prodomain BLP cleavage site is shown to make the prodomain a powerful stimulator of muscle growth when administered to adult mice. Thus, cleavage at this site is biologically important. We propose showing which BLP may be responsible for activating gdf-8 in vivo. Gdf-11 (BMP-11) and gdf-8 form a subfamily of TGF-b-like molecules based on sequence homologies in their mature regions. We have preliminary evidence that the gdf-11 propeptide is cleaved by BLPs. We propose showing that mature secreted gdf-11 noncovalently binds its prodomain, that BLPs cleave the prodomain to release and activate mature gdf-11, and that this occurs in vivo. Gdf-11 is an inhibitor of neural tissue formation. Therefore, characterizing the mechanisms for in vivo activation of gdfs 8 and 11 has important implications for how such activation might be blocked, and thus how muscle and nerve regeneration may be enhanced in musculo- and neuro-degenerative diseases. We also propose determining which BI-Ps may cleave extracellular BMP antagonists Chordin-like 1 and 2, which show much overall homology with Chordin and which show indications of being regulated via proteolysis. In addition, we present evidence that BLPs may be involved in processing members of the prolactin, growth hormone/placental lactogen family of hormones to produce specific 16 kDa product. We propose determining which of these hormones are cleaved by which BLPs, at which sites, and whether such cleavages occur in vivo. Previous reports indicate that 16 kDa products of these hormones to biologically important. Thus, determining how these fragments are formed is of potential importance in regulating human endocrine functions. Conditional knockout mice for BLP genes will be created, for in vivo portions of the projects described above, and for future studies of the tissue-specific roles of BLPs in development and homeostasis. Finally, we present evidence for and propose experiments to further determine in vivo roles for the precursor forms and prodomains of BLPs in development and homeostasis.